In the recent trend of higher picture quality and higher density of personal computer, Hi-Vision TV receiver, digital TV receiver and others, the deflecting frequency is widely used, and the frequency tends to be higher.
In these display devices using CRT, in particular, various proposals have been made relating to:
horizontal deflection, PA1 high voltage generating circuit, and PA1 control. PA1 feeds a horizontal synchronizing pulse to a deflection control circuit 14, and PA1 drives a horizontal deflecting transistor 2. PA1 passing a sawtooth type current into the deflecting yoke 5, and PA1 returning from end point to start point of scanning during the blanking period. PA1 stabilization of high voltage, PA1 simple constitution, PA1 efficient operation, and PA1 operation at low oscillating voltage. PA1 the switching element 10 is switched by the PWM signal synchronized at f [Hz], and PA1 the feedback system is composed so that the high voltage output may be uniform. PA1 two switching elements, PA1 synchronizing triangular wave oscillating circuit 63, and PA1 PWM comparator 64 and the circuit is complicated. PA1 switching loss due to two switching elements, and PA1 loss of damping circuit 66 and the efficiency is lowered. PA1 the stress to the switching element 27 is large, PA1 the loss increases, PA1 the oscillating current when turning on the switch is large, and PA1 image noise or malfunction may be caused. PA1 the efficiency is lowered, PA1 large parts must be used, and it is less economical, PA1 additional circuits are required, such as synchronizing triangular wave oscillating circuit 63 and PWM comparator 64, and PA1 setting of maximum ON time is complicated. They are same as explained in FIG. 11. PA1 the ON time more than the pulse width is not obtained, PA1 the horizontal deflecting operation frequency and high voltage maximum output power are lowered especially when the frequency is low, and PA1 the control range is narrow. In this circuit constitution, further, PA1 the blanking pulse width is very narrow as compared with the horizontal deflecting period, PA1 there is a non-saturation state in which switching is not secure, and PA1 the loss is increased. PA1 one switching element is used for high voltage control, PA1 the PWM switching control circuit is composed in a simple constitution while synchronizing with the operation frequency of the horizontal deflecting circuit, and PA1 the OFF time oscillating voltage and ON time oscillating current of the switching element are suppressed. PA1 The high voltage generating circuit of the invention comprises: PA1 a high voltage generating transformer having a primary winding and a high voltage generating winding, and PA1 a switching element. PA1 synchronizing switching means to the horizontal operation frequency, and PA1 high voltage stabilizing means, being a converter circuit for converting the blanking pulse winding voltage obtained from the deflecting transformer or deflecting yoke for composing the deflecting circuit into a comparative waveform for control for obtaining a specified switching ON time by the horizontal deflecting operation frequency, further comprising: PA1 a circuit for controlling the ON time of the switching element by changing the DC bias voltage of the comparative output waveform, and comparing with the threshold voltage of the comparator or switching element, and PA1 suppressing means of oscillating components.
The basic operation of the deflecting circuit and high voltage generating circuit in the CRT display device is described below.
FIG. 10 is an explanatory diagram of conventional deflecting circuit and high voltage generating function.
As shown in FIG. 10, a horizontal deflecting circuit (not shown)
The deflecting circuit is composed of a deflecting yoke 5, a damper diode 3, and a capacitor 4. The power source is supplied to the deflecting circuit through a deflecting transformer 8.
The horizontal deflecting circuit is used to deflect an electron beam in the horizontal direction.
During scanning period, the horizontal deflecting circuit realizes horizontal deflection by
The resonance pulse occurring in the blanking period is called a blanking pulse. A deflecting and high voltage integrated circuit for obtaining a high voltage output by adding a high voltage winding 61 to the deflecting transformer 8 is used in a general TV receiver.
However, the high voltage output is lowered by increase of electron beam current.
Accordingly, by generation of high voltage fluctuation, both amplitudes of horizontal deflection and vertical deflection fluctuate.
Further, this high voltage fluctuation causes image deformation.
As their solving means, the following two methods are known.
1) Deflecting and high voltage separated circuit system: The deflecting circuit and high voltage circuit are separately composed, and each circuit is controlled independently.
2) Deflecting and high voltage integrated circuit system. The high voltage is stabilized by minimizing effects of high voltage to the deflecting circuit.
Both systems require
FIG. 11, FIG. 12 and FIG. 13 show the prior art in the deflecting and high voltage separated circuit. FIG. 11 and FIG. 12 are explanatory diagrams of conventional high voltage generating circuit. FIG. 13 shows an example of operating voltage and current waveform of the conventional high voltage generating circuit.
In FIG. 11, one end of a primary winding 32 of a high voltage generating transformer 69 is connected to the drain of a switching element 27.
Other end of the primary winding 32 is connected to a step-down converter composed of a switching element 10, a flywheel diode 11, a smoothing capacitor 13, and an inductor 12.
By a signal from a deflecting control circuit 14, a synchronizing triangular wave generating circuit 63 is synchronized at f [Hz], and issues a triangular wave for comparison. The secondary side output voltage of the high voltage generating transformer 69 is divided by detecting resistances 45, 46. The divided voltages are fed into an error amplifier 35, and compared with a reference voltage 34. The output amplified by the error amplifier 35 is fed into a pulse width modulation (PWM) comparator 64 together with the triangular wave for comparison. The output of the PWM comparator 64 is connected to the gate of a switching element 10 through a drive circuit 65.
At the gate of the switching element 27, a specific drive pulse is supplied from the deflecting control circuit 14. At the primary side of the high voltage transformer 69, a damping circuit 66 composed of inductor, capacitor and resistance is connected in series to the primary winding 32. This damping circuit 66 is for suppressing the oscillating current due to resonance of the leakage inductance and distributed capacity.
The high voltage generating circuit of such circuit constitution is a step up/down DC/DC converter operating by two switching elements.
In this case,
In this constitution, the object of stabilization of high voltage output is achieved.
However, the constitution in FIG. 11 requires
The constitution in FIG. 11 is also accompanied by
The PWM operation by triangular wave can control in a wide range. However, it is complicated because it requires setting of maximum ON time and others.
An example of circuit using one switching element is shown in FIG. 12.
In FIG. 12, one end of the primary winding 32 of the high voltage generating transformer 69 is connected to the drain of the switching element 27. The deflecting circuit 62 issues a synchronizing signal of automatic frequency control (AFC) or the like to the synchronizing triangular wave oscillating circuit 63. The oscillating circuit 63 issues a triangular wave for comparison. The detection of high voltage and error amplifier circuit are same as in FIG. 11. Similarly, the output of the PWM comparator 64 drives the gate of the switching element 27 through the drive circuit 65. The control operation for stabilization of high voltage is same as in FIG. 11. However, the high voltage generating mode by switching is a discontinuous mode operation by a step-up converter.
The circuit in FIG. 12 is simple, using only one switching element. However, when the switch 27 is turned off, the circuit in FIG. 12 generates a flyback pulse. The high voltage winding supplies a high voltage in this OFF period (Toff). At this time, owing to the inductance of the primary winding 32, distributed capacity of high voltage winding, and capacity of the switching element 27, a violent oscillating voltage is generated as shown in FIG. 13. As a result, when the switch 27 is turned on, a high peak current flows instantly if the drain voltage is at the peak of the oscillating voltage.
This phenomenon causes image noise or adverse effects on control operation (oscillation, malfunction). The circuit in FIG. 12 has such defects.
Also in the circuit in FIG. 12,
To prevent these defects, the damping circuit 66 is connected to the primary circuit. However, its loss is as much as several watts.
Therefore, when the damping circuit 66 is connected to the primary circuit,
FIG. 14 shows a prior art of a deflecting and high voltage integrated circuit. This is an explanatory diagram of a conventional deflecting high voltage generating circuit. In the case of this circuit, a first high voltage generating transformer 60 is installed at one leg of a U-shaped core 53. In order to minimize the effects of high voltage fluctuations on the deflecting operation, it is operated to regenerate energy at power source +B from the primary winding 67 through a diode 68. A second high voltage corrective transformer 69 is cascade-connected to the low voltage side (grounding side) of this high voltage winding. A deflecting transformer winding 8 is placed at other leg of the U-shaped core 53. The deflecting circuit operates same as the circuit shown in FIG. 10. However, using the blanking pulse, the high voltage generating transformer 60 generates part of the high voltage. The circuit shown in FIG. 14 achieves the object by controlling the output voltage of the corrective transformer 69 in order to keep constant the high voltage output.
The operation of the high voltage stabilization by using the corrective transformer is explained below. A switching winding 9 is wound at the deflecting winding side. The blanking pulse of positive polarity (one end) of the switching winding 9 is connected to the gate of the switching element 27. The negative polarity side (other end) of the switching winding 9 is connected to the output of an inversion error amplifier 51 which operates on a negative power source. One end of the primary winding 32 of the corrective transformer 69 is connected to the power source +B', and other end of the primary winding 32 is connected to the drain of the switching element 27. The source of the switching element 27 is grounded. A rectifying circuit is connected to the output of the high voltage winding 39 of the secondary side, and the output voltage is applied to the low voltage side (grounding side) of the first high voltage generating transformer 60. As a result, the final high voltage output is the sum of the outputs of the two transformers. When the output voltage declines, the detection voltages divided by the detecting resistances 45, 46 are also lowered. Accordingly, the output of the inversion error amplifier 51 climbs up and becomes nearly zero volt. Consequently, the DC bias voltage of the winding 9 rises, and the voltage applied to the gate is raised. When the gate exceeds the threshold voltage, the switching element 27 is turned on. When the gate becomes lower than the threshold voltage, the switching element 27 is turned off. By this operation, the time (the ON time) surpassing the threshold voltage of the blanking pulse elevated in the DC bias voltage becomes longer. As a result, the output voltage of the corrective transformer 69 is raised, and continues to climb up until the final high voltage output reaches the specified voltage, thereby operating to stabilize.
This circuit constitution is simple because the blanking pulse which is the output of the winding 9 is used as the switching pulse and comparative waveform for PWM operation.
However, since the blanking pulse of the switching winding 9 is used for switching, the circuit constitution has demerits, that is:
This circuit constitution is small in the electric power handled by the corrective transformer, but generation of oscillating current and voltage is same as in the examples shown in FIG. 10, FIG. 11 and FIG. 12, and it is required to suppress.